Current practice in the installation of underground wiring involves the following steps: digging a trench in the ground; positioning at intervals along the trench a series of metal supports which provide upwardly-facing, generally U-shaped recesses for receiving a pipe; positioning in the trench, resting in the recesses of these supports, one or more plastic pipes through which the wiring will extend longitudinally; and then pouring concrete into the trench to solidify around the pipe and embed it securely in the trench. Typically, such underground pipes may be 2, 4, or 6 inches in diameter. The pipes extend between manholes in the ground which have openings in their side walls in alignment with the pipes. Each pipe should be held tightly against the manhole at the opening when the concrete is poured so that the wet concrete will not get into the end of the pipe and solidify inside the pipe. Prior to the present invention no entirely satisfactory and convenient arrangement has been provided for achieving this. As a consequence, frequently wet concrete has gotten into the end of the pipe and solidified inside the pipe, and has had to be removed later at great effort and expense.